Diaphragm or membrane valves are known in the art. Often a flexible diaphragm is secured between two mating surfaces in a valve body sometimes serving as a gasket or seal there between. The diaphragm forms two discrete chambers by completely separating two more or less symmetrical shallow indentations fabricated in each of the joined faces of the valve body. Often one of the chambers is connected by suitable ports or vents to a source of fluid under control pressure sufficient to cause the diaphragm to invert or reciprocate to come to bear against the surface of the mating indentations which comprising a second chamber. This second chamber is often ported to the exterior of the valve body by an inlet and outlet channel through which the controlled fluid under pressure flows through respective piping or tubing connected to the valve body. The control fluid flows through the valve chamber until pressure applied through the control chamber causes the diaphragm to deflect, cover one or both ports and thereby stop the flow.
Other valves commonly used to control the flow of fluids comprise spool valves and ball valves. In the operation of such valves, the spools or balls slide or rotate through seals which are compressed against them. Factors which can cause such valves to fail are the presence of abrasive solids in the control fluid, which solids cause wear on both the seals and the operating elements. Non-abrasive materials accumulating within a spool valve can obstruct the flow of control fluid through the valve or cause the spool to bind within the seals. For these reasons, spool and ball valves operate most reliably in controlling fluids from which solids and other contaminants have been removed by means such as filters. Provided the control fluid is maintained free of damaging contaminants and the filters, to, are maintained in functioning condition, spool or ball valves are relatively long lived. Even under good operating conditions, however, attrition on the seals is a meaningful factor when spool or ball valves are cycled continuously at short intervals, for example, when used in machines which dose liquid product.
With no mechanical moving parts, and no internal compression seals, diaphragm valves are relatively unaffected by solids or other contaminants in the control fluid passing through them or in the control fluid applied to operate the diaphragm. However, there are certain disadvantages inherent in conventional diaphragm valves commonly used. For example, should the diaphragm rupture, the valve fails. Moreover, the diaphragm must be operated by fluid under pressure often substantially greater than under which the control fluid is passing through the valve.
For example, in the closed position, most of the diaphragm is supported by the floor of the valve chamber. However, those areas of the diaphragm which lie over port(s) being unsupported, must resist the dynamic forces exerted by control pressure each time the valve is cycled. Should the diaphragm become worn or perforated, fluid from the control chamber may become mixed with fluid in the valve chamber. In certain applications, contamination of the fluid passing through the valve chamber can have serious consequences. Furthermore, when diaphragms are used to control volumetric metering devices, leakage through the diaphragm can cause variations in the volumes dosed. Also, in devices of this kind, a random flexure of the unsupported diaphragm causes varying volumes of liquid to be retained in the valve chamber when the valve is closed, thereby affecting the volume of the dose. Inasmuch as the valve will continue to operate, nothwithstanding a minor diaphragm leak, the difficulty of detecting such a leak in a conventional valve could be tantamount to serious malfunction of the device in which the valve is functioning. This is a meaningful consideration in applications where product purity and/or the true volume of discharge are meaningful considerations.
United Kingdom patent application GB No. 2,020,786A filed May 11, 1979 describes a double diaphragm valve which has certain advantages over prior art single diaphragm valves. That patent describes a ring structure which lies between two specially formed diaphragms of resilient material. Such diaphragm valves are an improvement over single diaphragm valves in certain applications.